Free radical polymerization is by far the most widely used chain polymerization technique for industrial applications. These industrial applications include, for example, thin films, coatings, paints, adhesives, optics, dental filling, sealing compound, and stereo-lithography. These reactions offer many advantages over other polymerizations, including 1) high reaction rates, 2) insensitivity to impurities (compared to anionic and cationic polymerizations), and 3) a wide selection of commercially available monomers and oligomers.
Control of molecular weight and end groups (functionalities) is currently accomplished by living anionic polymerization. The active centers in anionic polymerizations are highly reactive carbanions. The reactions carry on until all the monomer has been consumed or the reaction is quenched using water or alcohol. However, these reactions are highly sensitive to oxygen and proton donors (water, alcohols, etc.), and, therefore, it is necessary to exclude any impurities during reaction, which can be a difficult process. Relatively few monomers undergo living anionic polymerization, thereby limiting the polymers that can be formed using this approach.
Emulsion polymerization (macroemulsion polymerization) has been used in industrial processes for water-insoluble and sparingly soluble monomers. In emulsion polymerization monomer is located in monomer droplets, inactive micelles containing monomer, active micelles that become polymer particles where polymerization occurs, and as solute in aqueous phase.
Microemulsion polymerization differs from emulsion polymerization in that the microemulsion contains no monomer droplets and no inactive micelles. Another difference is that all the initiator in a microemulsion exists in the microemulsion droplets so that polymerization only occurs in the monomer reservoir encapsulated in the particle. Microemulsions are also optically transparent.
A number of investigators have studied polymerizations carried out in microemulsions wherein the polymerizable monomer is dispersed in water (Morgan, J. D., Kaler, E. W., “Particle Size and Monomer Partitioning in Microemulsion Polymerization. 1. Calculation of the Particle Size Distribution,” Macromolecules, 31, 3197-3202 (1998); Morgan, J. D., Lusvardi, K. M., Kaler, E. W., “Kinetics and Mechanism of Microemulsion Polymerization of Hexyl Methacrylate,” Macromolecules, 30(7), 1897-1905 (1997); Kuo, P-L., Turro, N. J., Tseng, C-M, El-Aaseer, M. S., Vanderhoff, J. L., “Photoinitiated Polymerization of Styrene in Microemulsions,” Macromolecules, 20(6), 1216-1221 (1987); Paul, B. K., Moulik, S. P., “Microemulsions: An Overview,” J. of Dispersion Science and Technology, 18(4), 301-367 (1997); Moulik, S. P., Paul, B. K., “Structure, Dynamics and Transport Properties of Microemulsions,” Advances in Colloid and Interface Science, 78, 99-195 (1998); Co, C. C., Cotts, P., Burauer, S., Vries, R. D., Kaler, E. W., “Microemulsion Polymerization. 3. Molecular Weight and Particle Size Distributions,” Macromolecules, 34, 3245-3254 (2001); Capek, I., “Photopolymerizations of Butyl Acrylate Microemulsion. Effect of Reaction Conditions and Additives on Fates of Desorbed Radicals,” Polymer Journal, 28(5), 400-406 (1996); Capek, I., Fouassier, J. P., “Kinetics of Photopolymerization of Butyl Acrylate in Direct Micelles,” Eur. Poly. J., 33(2), 173-181 (1997); Capek, I., Potisk, P., “Microemulsion and Emulsion Polymerization of Butyl Acrylate-I. Effect of the Initiator Type and Temperature,” Eur. Polym. J., 31(12), 1269-1277 (1995)). Most of the investigations in the literature have reported thermal polymerizations of microemulsions (Morgan, et al. (1998); Morgan, et al. (1997); Paul, et al (1997); Moulik, et al. (1998); Co, et al. (2001)), and there have been only a few reported of photopolymerizations in microemulsion systems (Capek, I., et al. (1996); Capek, I., et al. (1997); Capek, I., et al. (1995); Kuo, et al. (1987)). These investigators have focused their research on the study of kinetics and mechanisms of reaction, but none have utilized it as a tool to predict and regulate the polymer architecture.
The thermal polymerization studies reported in the literature were motivated by the fact that the microemulsion polymerizations offer better control on the system parameters and are viable with most of the monomers relative to the more conventional emulsion polymerizations (Morgan, et al. (1997)). The studies reported to date have focused primarily on methacrylate and styrene monomers (Kuo, P-L., et al. (1987)) and have focused on creating the phase diagrams for the monomer-in-water microemulsions (Paul, B. K., et al. (1997); Moulik, S. P., et al. (1998)) and on describing the kinetics of the polymerizations (Co, C. C., et al. (2001)). Studies of thermally-initiated microemulsion polymerizations have revealed that this technique yields information about formation of the microemulsions and effect of various classes of surfactants and additives. Information about various techniques of characterization of microemulsions has also been revealed. The thermal polymerizations are generally initiated using either water-soluble initiators, such as ammonium peroxodisulfate, or monomer-soluble initiators, such as azoisobutyronitrile (AIBN).
While the vast majority of the papers on microemulsion polymerizations in the literature focus on thermally-initiated polymerizations, there are a few reports of photoinitiated microemulsion polymerizations. These papers report investigation of photopolymerization of microemulsions by initiation with UV light and have investigated the effect of various additives on the rate of polymerization and the final conversion of monomer (Capek, I., et al. (1996); Capek, I., et al. (1997); Capek, I., et al. (1995)).
Kuo, et al. (1987) photopolymerized styrene in an oil/water microemulsion using dibenzyl ketone (DBK) as an oil-soluble initiator. The polymerization was initiated by UV light. The degree of polymerization and the rate of polymerization were studied as a function of initiator concentration and light intensity. The mechanism of polymerization in microemulsions was discussed on the basis of polymerization rate and particle size. The study did not include choice of end groups for the styrene polymer.
Capek, et al. (1997) looked at the kinetics of photopolymerization of butyl acrylate in an oil/water microemulsion. The polymerization was initiated by UV light. Change in molecular weight relative to monomer and emulsifier concentration was studied. Rate of polymerization was found to be proportional to light intensity. This study did not involve choice of end groups for the butyl acrylate polymer.
In the current invention, various properties offered by microemulsions and photopolymerizations can be utilized to custom make polymers with a higher degree of control of the polymer molecular weight. Also, the polymers can be customized with desired end groups. The invention uses the advantages offered by microemulsions and photopolymerizations to produce commercially useful polymers.
None of the above-cited documents disclose compounds, methods, etc. such as those disclosed or claimed herein.